Localization patterns of speech and language errors during awake brain surgery: a systematic review

Awake craniotomy with direct electrical stimulation (DES) is the standard treatment for patients with eloquent area gliomas. DES detects speech and language errors, which indicate functional boundaries that must be maintained to preserve quality of life. During DES, traditional object naming or other linguistic tasks such as tasks from the Dutch Linguistic Intraoperative Protocol (DuLIP) can be used. It is not fully clear which speech and language errors occur in which brain locations. To provide an overview and to update DuLIP, a systematic review was conducted in which 102 studies were included, reporting on speech and language errors and the corresponding brain locations during awake craniotomy with DES in adult glioma patients up until 6 July 2020. The current findings provide a crude overview on language localization. Even though subcortical areas are in general less often investigated intraoperatively, still 40% out of all errors was reported at the subcortical level and almost 60% at the cortical level. Rudimentary localization patterns for different error types were observed and compared to the dual-stream model of language processing and the DuLIP model. While most patterns were similar compared to the models, additional locations were identified for articulation/motor speech, phonology, reading, and writing. Based on these patterns, we propose an updated DuLIP model. This model can be applied for a more adequate “location-to-function” language task selection to assess different linguistic functions during awake craniotomy, to possibly improve intraoperative language monitoring. This could result in a better postoperative language outcome in the future. Supplementary Information The online version contains supplementary material available at 10.1007/s10143-022-01943-9.

Supplementary Information 3. Explanation of the structure of the data A. Second analyses: calculation For each data set (except for the excluded 4) and each paraphasia type separately, the percentage of occurrence per location was calculated based on all occurrences of that paraphasia (cortically and subcortically). Example: in data set 1, speech arrest occurred 6 times in the PrG. In total, 10 speech arrests were found in this data set (cortically and subcortically). Based on this total, the occurrence of speech arrest in the PrG is calculated: ((6/10)*100=) 60%. Note: these numbers are for illustrative purposes only and do not reflect existing data.

B. Second analyses: visualization
The calculated percentages (see A) were used to compute cortical (Figure 3, 4) and subcortical ( Figure 5) plots. A separate cortical plot was computed for each data set and paraphasia type (three plots per paraphasia type). Example: in data set 1, anomia occurred 9 times in total (cortically and subcortically, see black matching circle in A and B) and 5 times at the cortical level (dashed black circle in A and B). Anomia occurred twice at the IFOF (blue circle in A and B), which corresponds to 22.2% (red circle in A and B). Note: even though one plot visualized either cortical or subcortical areas, the used totals and percentages were based on BOTH levels (see B).

C. Third analyses
It was calculated how often each paraphasia type occurred cortically and subcortically per data set. A division was made between general subcortical areas and tracts. For example, anomia from data set 1 (see A, copied below) occurred (3+2=)5 times cortically and (2+2=)4 times subcortically, of which 2 times at the general level and 2 times at the tract level (see Figure 7 for actual plot). In total, anomia occurred 9 times in this data set, which can be seen in the right plot on the y-axis (absolute number of errors). Each data set and paraphasia type was seen as a subset (plot below was seen as 1 subset). The subset below contained more cortical (5) than subcortical errors (4). Additionally, it contained subcortical general and tract locations. D. Summary -The percentages/totals are based on cortical and subcortical locations, even though one plot visualised either cortical or subcortical locations.
-The percentages from the cortical plots and subcortical plot do not add up to 100%, since 1) some cortical areas are unplottable with the DKT-atlas (see 2.4.4.) and are thus not shown in the plot and 2) only the subcortical tracts and not the general subcortical areas are displayed in Figure 5 (see 2.4.2.).
-Note: for analyses 1, a comparable structure was followed. However, the frequencies of occurrence per location (cortical and subcortical) were combined for all data sets and paraphasia types (see Supplementary Materials 4 for DKT-atlas compatible cortical frequencies). Additionally, these percentages were only visualized in a cortical plot (see Figure 2) and not in a subcortical or division plot, while the totals were again based on cortical and subcortical data.
Supplementary Information 4: The brain locations in the current data and the converted brain locations compatible with the (lateral) DKT-atlas.